1. Technical Field
The invention relates to chairs, particularly to chair backs.
2. Related Art
Office chairs with a cushion elevation mechanism and/or flexibly tiltable back have been very popular. A flexibly tiltable back is a very important mechanism because it makes users very comfortable. FIG. 1 shows a typical mechanism of flexibly tiltable back. Many chairs are provided with a flexible back with tilt flexibility, as shown in FIG. 1, they use a rotation mechanism 1 to make the back 11 tiltable. However, the tilting angle of the back 11 is limited the rotary angle range of the support arm 13 connected to the cushion 12. In other words, the back 11 cannot offer a larger angle range of tilting because it moves with the support arm 13 only. This limits comfort of users when they sit on the chair.